As is known, crampons are fixed under the sole of mountain boots to improve the grip and stability of the user on ground or walls covered with packed snow or ice.
Currently known crampons normally comprise a front and a rear plate, which are fixed respectively under the front and rear portion of the sole of the boot, are normally hinged to each other to allow the structure a certain amount of flexibility when walking, and have a number of bottom spikes projecting from the peripheral edge of the two plates, in the opposite direction to the sole of the boot, so as to penetrate the layer of ice or packed snow when the boot rests on the ground.
Crampons also comprise a number of front spikes projecting frontwards from the front edge of the front plate, and by which to drive the toe of the boot into the layer of ice or packed snow when climbing substantially vertical walls.
As is known, crampons are currently fixed to the sole of mountain boots by means of a front fastening bracket and a rear fastening device fixed to the front and rear plate respectively.
The front fastening bracket locks the toe of the boot to the front plate of the crampon, and is defined by a U-shaped metal bar hinged at both ends to the front plate of the crampon to form, with the front plate, a closed ring engaged by the front portion of the sole of the boot.
The rear fastening device locks the rear portion of the boot to the rear plate of the crampon, and comprises a lock lever which clamps onto the heel of the boot to keep the toe of the boot resting against the front fastening bracket; and a supporting bracket connecting the lock lever to the rear plate.
Crampons also comprise a safety strap which is fastened about the instep of the boot to prevent the lock lever of the rear fastening device from working out of the lock position clamped onto the heel of the boot to keep the toe of the boot resting against the front fastening bracket.
Crampons of the above type have the major drawback of working loose relatively easily when used on mountain boots with particularly soft vamps.
Mountain boots with soft vamps, in fact, are extremely flexible, so that the tip of the sole may easily work loose from the front fastening bracket of the crampon, thus resulting in total or partial detachment of the crampon from the boot.
To eliminate the above drawback, known crampons are equipped with auxiliary straps, which are fastened about the vamp of the boot, at the forefoot and instep, to fasten the front plate of the crampon more securely to the sole of the boot.
Securing the crampon to the boot using auxiliary straps, however, conflicts with the need to ensure long-term comfort.
In the case of particularly soft vamps, the auxiliary straps exert considerable pressure on the vamp, which may impair circulation of the blood to the foot, thus resulting, when walking for prolonged periods, in severe fatigue and possibly also inflammation of the foot.